Engine temperature swings 220 then down to 150??

Ugh!! my 350 lh crusader model 270 raw water cooled has a temperature swing (verified by placing hand in exhaust stream while running on hose). i have replaced raw water pump, thermostat, releif valve.... any ideas??

Welcome to ME.com!

a bit more detail would enable us to provide some ideas.....what you provided is a bit sparse....none of us are there so you are the "eyes and ears".....

How old are the engines? what do you do to induce the problem? how long has it been going on? any recent servicing done? salt water operation? how old are the elbows?

Finally, 'throwing parts' at a problem can be a very expensive approach....better to diagnosis exactly what is wrong and then replace what needs to be replaced....

hi.... son't know if you got last thread engine is 1993 installed in a 22' C hawk... salt water cooled. replaced risers, manifolds in 2015... ran well no temp problems... flushed system in late 2015 .... stored on trailer after flushing with fresh watre and i always stow with system full of anti freeze.
the boat sat at slip most of last summer ... used infrequently by my son as i battled and beat cancer!! it started to show the temperature problems mid june.. replaced thermostat, and nylon relief valve... no change hauled and winterized. last week removed raw water pump and found that the carbon bearing had cracked and wiped out the casing ugh... installed a new sherwood pump and ran on hose on trailer in yard.... much to my dismay Same Problem... was able to put my hand in the exhaust cooling stream and could actually feel the temperature fluxutation???? any help would be greatly appreciated! thanks ... gary

congrats on winning the battle!

curious as to how you hook up the hose while on the trailer....??? how did you winterize the engine with the failed pump???

with raw water cooled sterndrives, running on the hose, it is not unusual to be able to feel the temp change as the thermostat opens and closes....

is the strainer cap on tight, with a good gasket??? all the raw water hose clamps tight?

do you have access to some 1.25" ID clear vinyl tube?? can be useful for temporary use in troubleshooting cooling issues?

finally, is the oil level ok and the oil 'normal' in color?

Hi Mark.... the boat is an inboard... a great job of putting it in the C Hawk has hard piped stainless hose connection and valving to run on a hose!! sooo i can also utilize the connection to siphon antifreeze when i winterize... makes for an easy winterization in the driveway!! i have checked the hoses and will double check on monday if it ever stops raining here in CT the strainer is a bronze cased/stainless screen which i will recheck .... oil level is aok and clean....i may try bypassing the suction line and see if the problem exists with direct coupling into the raw water pump?? i am an old submarine (USS NAUTILUS SSN571) machinists mate and have always done all work on this boat (changing manifolds,etc) but this one has me stumped.... maybe a senior thing ?? )

hope the custom plumbing has really good ball valves and they are seated correctly....the Sherwood pump is like any other vaned pump; they work great with an airfree supply of water.....any air leak will remain in the cooling water and, as I'm sure you are aware, aerated water don't remove heat real good....the clear tube can be used to detect an aerated flow downstream of the pump....

Only other warning is not to operate the engine using the hose at any rpm above idle.....very few hose bibs can keep up with an adequate supply if the throttle is advanced....

one other thing - are all the 'tabs' on the riser/elbow gaskets in the 11 o'clock & 1 o'clock positions? and none are 'single tabbed' gaskets??

hi Mark... i am working on boat today had to go to a funeral on fishers island on sunday..thanks for input ... i will keep youi nformed